Can't connect to MDBT42Q module reliably

OK, I think I figured it out. I'm using pins D9 & D10 to talk to a I2C device, and according to this thread I needed to disable NFC first. Now it appears to work just fine, and I can even retrieve values from the I2C device (an SHT40 temperature/humidity sensor for which I wrote an Espruino library)

I would still like to know what the best way is to solder these modules? My steps are as follows:

1. Tape the module to the PCB
   
2. Add lots of flux
   
3. Put some solder on soldering iron and drag it across the pins
   
4. Continue doing this until it looks like all connections have been made
   
5. Use solder wick to clean up any bridges
   
6. Clean up the flux with some IPA
   
   

I skipped step 6 last night and this morning my second board stopped working. After cleaning the board it works again, which made me realise that my water-soluble flux is not no-clean flux and should be cleaned.